Platelets attenuate oxidant-induced permeability in endothelial monolayers: glutathione-dependent mechanisms

Encapsulated platelets modulate kupffer cell activation and reduce oxidative stress in a model of acute liver failure

Acute liver failure (ALF) is characterized by massive hepatocyte cell death. Kupffer cells (KC) are the first cells to be activated after liver injury. They secrete cytokines and produce reactive oxygen species, leading to apoptosis of hepatocytes. In a previous study, we showed that encapsulated platelets (PLTs) increase survival in a model of ALF. Here, we investigate how PLTs exert their beneficial effect. Wistar rats submitted to 90% hepatectomy were treated with PLTs encapsulated in sodium alginate or empty capsules. Animals were euthanized at 6, 12, 24, 48, and 72 hours after hepatectomy, and livers were collected to assess oxidative stress, caspase activity, and gene expression related to oxidative stress or liver function. The number of KCs in the remnant liver was evaluated. Interaction of encapsulated PLTs and KCs was investigated using a coculture system. PLTs increase superoxide dismutase and catalase activity and reduce lipid peroxidation. In addition, caspase 3 activity was reduced in animals receiving encapsulated PLTs at 48 and 72 hours. Gene expression of endothelial nitric oxide synthase and nuclear factor kappa B were elevated in the PLT group at each time point analyzed. Gene expression of albumin and factor V also increased in the PLT group. The number of KCs in the PLT group returned to normal levels at 12 hours but remained elevated in the control group until 72 hours. Finally, PLTs modulate interleukin (IL) 6 and IL10 expression in KCs after 24 hours of coculture. In conclusion, these results indicate that PLTs interact with KCs in this model and exert their beneficial effect through reduction of oxidative stress that results in healthier hepatocytes and decreased apoptosis. Liver Transplantation 22 1562-1572 2016 AASLD.

The activity of antioxidant enzymes in blood platelets in different types of renal replacement therapy: a cross-sectional study

PURPOSE

The changes in redox status characterise physiological platelet activation. Increased oxidative stress in chronic kidney disease (CKD) associated with uremic toxicity and procedures of renal replacement therapy leads to the impairment of antioxidant properties of platelets. It may contribute to thrombosis and cardiovascular complications increasing morbidity and mortality among the CKD patients. The object of the research was to assess the influence of conservative treatment, peritoneal dialysis and haemodialysis on platelet prooxidative-antioxidative balance.

METHODS

The examined group consisted of 122 patients: 37 on regular haemodialysis (HD), 23 on peritoneal dialysis (PD) and 62 on conservative treatment with CKD stages 3-5 (CKD3-5). The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione transpherase (GST) in platelets were obtained using kinetic methods. The spectrophotometric method established the concentrations of reduced glutathione (GSH).

RESULTS

SOD activity in PD differs significantly from CKD3-5 (4.96 vs 1.66; p < 0.0001). CAT activity assessed in PD and CKD3-5 was significantly different from HD (0.82 and 0.8 vs 0.52 before and 0.35 after HD, respectively). GST activity reached the highest value in PD (1.62), and it was significantly different from CKD3-5 (0.23) and HD before haemodialysis (0.11). During haemodialysis therapy, there was a considerable increase in GST activity (0.11 vs 0.3; p = 0.02) and decrease in SOD activity (from 3.41 to 2.27; p = 0.01). The highest GSH concentrations were obtained in CKD3-5 and differ significantly from HD (4.12 vs 2.01; p = 0.02).

CONCLUSIONS

The type of treatment, age and duration of renal replacement therapy determined significant changes in platelet antioxidative enzymes activities and concentration of GSH, which may enhance the thrombotic complications. PD is associated with lower platelet oxidative stress.

Platelet increases survival in a model of 90% hepatectomy in rats

BACKGROUND & AIMS

Ninety per cent hepatectomy in rodents is a model for acute liver failure. It has been reported that platelets have a strong effect enhancing liver regeneration, because of the production of several growth factors such as serotonin. The aim of this study was to investigate the role of microencapsulated platelets on 90% hepatectomy in rats.

METHODS

Platelets (PLT) were microencapsulated in sodium alginate and implanted in the peritoneum of rats after 90% partial hepatectomy (PH). Control group received empty capsules (EC). Animals were euthanized at 6, 12, 24, 48 and 72 h post PH (n=9-12/group/time) to evaluate liver regeneration rate, mitotic index, liver content, serum and tissue levels of Interleukin 6 (IL-6) and serotonin and its receptor 5-hydroxytryptamine type 2B (5Ht2b). Survival rate in 10 days was evaluated in a different set of animals (n=20/group).

RESULTS

Platelets group showed the highest survival rate despite the lowest liver regeneration rate at any time point. Mitotic and BrdU index showed no difference between groups. However, the number of hepatocytes was higher and the internuclear distance was shorter for PLT group. Liver dry weight was similar in both groups indicating that water was the main responsible factor for the weight difference. Gene expression of IL-6 in the liver was significantly higher in EC group 6 h after PH, whereas 5Ht2b was up-regulated at 72 h in PLT group.

CONCLUSIONS

Platelets enhance survival of animals with 90% PH, probably by an early protective effect on hepatocytes and the increase in growth factor receptors.

Regulation of coronary venular barrier function by blood borne inflammatory mediators and pharmacological tools: insights from novel microvascular wall models

We hypothesized that postcapillary venules play a central role in the control of the tightness of the coronary system as a whole, particularly under inflammatory conditions. Sandwich cultures of endothelial cells and pericytes of precapillary arteriolar or postcapillary venular origin from human myocardium as models of the respective vascular walls (sandwich cultures of precapillary arteriolar or postcapillary venular origin) were exposed to thrombin and components of the acutely activatable inflammatory system, and their hydraulic conductivity ( LP) was registered. LP of SC-PAO remained low under all conditions (3.24 ± 0.52·10−8cm·s−1·cmH2O−1). In contrast, in the venular wall model, PGE2, platelet-activating factor (PAF), leukotriene B4 (LTB4), IL-6, and IL-8 induced a prompt, concentration-dependent, up to 10-fold increase in LP with synergistic support when combined. PAF and LTB4 released by metabolically cooperating platelets, and polymorphonuclear leucocytes (PMNs) caused selectively venular endothelial cells to contract and to open their clefts widely. This breakdown of the barrier function was preventable and even reversible within 6–8 h by the presence of 50 μM quercetin glucuronide (QG). LTB4 synthesis was facilitated by biochemical involvement of erythrocytes. Platelets segregated in the arterioles and PMNs in the venules of blood-perfused human myocardium (histological studies on donor hearts refused for heart transplantation). Extrapolating these findings to the coronary microcirculation in vivo would imply that the latter's complex functionality after accumulation of blood borne inflammatory mediators can change rapidly due to selective breakdown of the postcapillary venular barrier. The resulting inflammatory edema and venulo-thrombosis will severely impair myocardial performance. The protection afforded by QG could be of particular relevance in the context of cardiosurgical intervention.

Platelet function in sepsis

OBJECTIVE

To evaluate platelet function in sepsis.

DATA SOURCES

The MEDLINE database and bibliographies of selected articles.

DATA SYNTHESIS

The common occurrence of thrombocytopenia in critically ill patients has been recognized for many years and is known to be associated with an increased mortality rate. Platelet function can be divided into four areas: activation, adhesion, aggregation, and secretion. Studies have found that activated platelets secrete key components of the coagulation and inflammatory cascades and are involved in the regulation of vascular tone. However, studies on platelet function in sepsis have been scarce, and their data are often conflicting. In sepsis, aggregation of circulating platelets seems to be reduced, yet platelet receptors are present in normal amounts.

CONCLUSIONS

Platelets play a complex role in sepsis; they are able to modulate not only their own function but also that of cells around them. Further study is needed to better define the precise mechanisms and effects of platelet activation in sepsis and to determine the benefits and risks of inhibiting platelet function.